There's no reason the bearings won't hold up spinning a small fan direct
drive. Spinning a big prop is a different matter.


That previous discussion you are alluding to about a direct drive 13B
engine, was where I proposed supercharging the engine to make the same
power at 3500 rpm as it makes at 6000 with a redrive. That's where the
problem with the bearings comes in because the much higher combustion
pressures at low rpm would be hard on the bearings.

With a fan engine you have a completely different scenario. You are
spinning the engine at 6000 rpm or more just like you would in a car and
driving a little fan with small mass moment.

When you asked about the single-rotor engine in the mini-imp I assumed
you were thinking ducted fan, in which case I think it would work just
fine. But if you are thinking propeller and long driveshaft, Paul is
right, it's going to run into vibration problems big time.


Regards,

Gordon.




George ( down under) is referring to the thrust bearings
in the 13B. Perry Mick destroyed a set after a few years
with his direct drive set up. They are not designed to withstand
continuous thrust.

Charley Airseman did extensive experimentation with a shaft
direct drive and eventually abandoned it and went with a very large
diameter composite prop extension.

Paul Lamar ...No rotor no motor.

Gordon,
Charley A's damper is a serious looking damper as well. I may be wrong but
he probably has serious bearings before the prop to absorb thrust and
gyroscopic loads.
Personally I would consider having both these in any direct drive regardless
of the size of the prop or configuration - duct or no duct.
Isolate the engine from the prop loads and your off to a good start.
Just suggestions mind you!
George ( down under)

The aft ball bearing takes the thrust in the shaft drive
version. He relies on the Soob thrust bearing in the
large diameter composite crankshaft extension version so far.
We shall see how long that lasts.

Paul Lamar


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